TMN Information Models - M.3100, G.803

Understanding ITU-T M.3100

Applying OSI Network Management to Telecommunications Networks

Perhaps one of the more popular applications of OSI network management can be found in the world of Telecommunications Management Networks (TMN). Much of the lower layer modeling provided within TMN is based on objects specified in M.3100. M.3100 in turn bases much of its terminology on the networking nomenclature defined for the Synchronous Digital Hierarchy (SDH) by G.803. Data networkers beware! Some of the terminology used to describe SDH can be a bit confusing at first, so pay attention to the details. You'll find that concepts such as connections and acronyms such as TCP have a completely new meaning. In keeping with the flavor of the relationship of these standards, we'll first review the general concepts (non-SDH specific) defined in G.803, and follow up with a discussion of the objects in M.3100.

G.803 - Defining a framework for modeling synchronous networks

Much of the information presented in the models of M.3100 are based on concepts defined in G.803. Through this recommendation, standard forms are provided for the definition of virtual objects within the telecommunications system. Figure 1. from G.803 depicts many of the components and their relationship in providing multiple layers of communications service. The ever-popular Client/Server model is used as a paradigm for describing the relationship between the layers of synchronous networks, with the client layer traffic being carried over transport services provided by the Server Layer.

Two important types of transport entities, trails and connections, are used to transfer information within the framework of the client and server layers. A trail, as shown in Figure 1, is responsible for managing the transfer of information through one or more client layers via "access points." A trail consists of trail termination functions that interact via a network connection. Connections, on the other hand, are used to transfer information between connection points; multiple connections can be used to support a single trail within a layer. As can be seen in the figure, a single layer can contain multiple connections that serve the information transport needs of the related client layer.

And just what are these other gizmos in the figure? you ask. There are several other components in the general framework defined by G.803. As can be seen in the figure, the objects include: If you are developing a TMN supportable model for managing equipment that you are developing, these concepts are invaluable. As we will now see, this terminology is a core element of the M.3100 object model that is one of the standard components of TMN management architectures.

Figure 1 - Example of functional model fragment (from ITU-T Recommendation G.803)

M.3100 Objects

With the architecture defined in G.803, you can now apply these concepts as managed objects. By describing the major system objects in GDMO using the G.803 framework, the object model can directly map into a familiar framework. Faults can be correlated to standard system objects ranging from the point of attachment within a server layer to the trail within the client layer; ideally, when a service affecting problem occurs, the source of the fault can be identified for remedial action, and the effected client services can be reallocated to the appropriate server trails. Configuration management is facilitated through providing standard mechanisms for provisioning and identifying fielded equipment and their configurations.

M.3100 takes the information developed to support the SDH models (in G.803), and adds several additional managed object classes that provide a baseline for developing application specific models. By using the M.3100 classes, integration of information models into the larger scale enterprise vision is possible. As a "Generic Information Model," M.3100 provides generally useful object classes that can be applied to support the TMN architecture. If, for example, you are developing a mega-switch gizmo with proprietary gizmo circuits, plan on using M.3100 as a model for breaking down your proprietary gizmo into the appropriate components. Through the classes defined in M.3100 uniform mechanisms are provided to support fault, configuration, performance, security and accounting management.

The M.3100 specification is organized into 6 "fragments" that combine to form the Generic information model. There are both direct containment relationships between the fragments along with associative peer relationships. The 6 fragments defined within M.3100 are: As you can see, through these fragments, M.3100 provides a set of objects to identify network topologies from several perspectives, and to provide the standard management functions. Figure 2 shows the inheritance relationship of many of the main objects required to support the M.3100 functional fragments. If you have had an opportunity to read some of the earlier articles in this series, you may notice that many of these classes of objects are direct references to X.721. No need to reinvent the wheel here. The goal is to provide a useful framework for organizing network management services. The remainder of the objects in the diagram are defined in the M.3100 specification.

Figure 2 - M.3100 Object Inheritance Hierarchy (Main Fragment)

Figure 3 - M.3100 Object Inheritance Hierarchy (Event Fragment)

The majority of the objects defined within M.3100 are self-evident in the context of the SDH system architecture definitions. There are some interesting issues in developing systems that implement these objects. For example, the termination point objects can be automatically instantiated by the managed element, or on the direction of the element management layer. Similarly, the establishment of associations between the termination points and their parent connections and trails is a matter requiring distributed knowledge.

Figure 4 - Containment Hierarchy (Sample Fragment)

As an example of how the objects can be distributed across the system, take a case in which there is a system requirement to isolate and recover from a fault within a finite time period. In the case of a layered solution as described by these standards, error conditions are likely to be identified by several objects in managed elements throughout the system. If the management information network has sufficient capacity to quickly report the fault conditions to a central arbiter responsible for network layer management functions, it is simplest to let the network layer manager handle and recover from the fault. However, if fault remediation services require a recovery time shorter than can be reasonably expected from the management network, it is likely that copies of the layer management objects may be distributed throughout the network. Since the standards do not constrain the implementation in these areas, solutions to these issues can be left to the system implementers.

As you can see, their is a broad selection of standards that are targeted toward assisting in the development of TMN based solutions. Within the last few years, the market for software components that assist in the realization of TMN products and management systems has entered a maturation process. Many major telecommunications carriers have entered into significant commitments to fielding and implementing TMN based management architectures. If you are developing equipment that may be targeted towards this market, and plan on offering your products to these customers, the development of Q3 capable interfaces that provide an appropriate set of objects based on M.3100 is worth serious consideration.